Stephen Poulston

Regeneration of NOx trap catalysts

We have investigated the regeneration of a nitrated or sulphated model Pt/Ba-based NO x trap catalyst using different reductants. H 2 was found to be more effective at regenerating the NO x storage activity especially at lower temperature, but more importantly over the entire temperature window after catalyst ageing. When the model NO x storage catalyst is sulphated in SO 2 under lean conditions at 650 °C almost complete deactivation can be seen. Complete regeneration was not achieved, even under rich conditions at 800 °C in 10% H 2 /He. Barium sulphate formed after the high temperature ageing was partly converted to barium sulphide on reduction. However, if the H 2 reduced sample was exposed to a rich condition in a gas mixture containing CO 2 at 650 °C, the storage activity can be recovered. Under these rich conditions the S 2- species becomes less stable than the CO 3 2-, which is active for storing NO x . Samples which were lean aged in air containing 60 ppm SO 2 at <600°C, after regeneration at λ = 0.95 at 650°C, have a similar activity window to a fresh catalyst. It is, therefore, important that CO 2 is present during the rich regenerations of the sulphated model samples (as of course it would be under real conditions), as suppression of carbonate formation can lead to sulphide formation which is inactive for NO x storage.

A New Palladium-Based Ethylene Scavenger to Control Ethylene-Induced Ripening of Climacteric Fruit

A novel palladium-promoted zeolite material with a significant ethylene adsorption capacity at room temperature is described. It was characterised by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and transmission electron microscopy (TEM) to show palladium particles dispersed over the support. Initial measurements of the ethylene adsorption capacity were conducted with a synthetic gas stream at a higher ethylene concentration than would normally be encountered in fruit/vegetable storage, in order to obtain an accelerated testing protocol. Further laboratory-based trials on fruit samples show that the palladiumpromoted zeolite material can be effective as an ethylene scavenger to prolong the shelf-life of fresh fruits.

Development of a new palladium-based ethylene scavenger

A new palladium-promoted material was discovered with significant ethylene adsorption capacity. The material effectively scavenged exogenously administered and/or endogenously produced ethylene by climacteric fruit. Corresponding inhibition of ethylene-induced ripening was observed.